This invention relates to disposable mixing containers for separate prepackaging of ingredients such as mercury and silver alloy. These ingredients are stored in separate chambers of the container and may be combined and mixed just prior to use.
Dental amalgam of silver alloy and mercury must be prepared just prior to use in a precise formulation. These twin requirements have in the past imposed difficulties upon dental surgeons, who were forced to compound the amalgam themselves, a time-consuming and hazardous task because of the difficulties and dangers inherent in the manipulation of mercury. The accurate measurement of mercury also requires expensive equipment, thus imposing an economic burden on the individual dental surgeon who prepared his own silver amalgam. Their problems have lead to the development of various disposable containers for prepackaging measured amounts of mercury and silver alloy so that they may be mixed just prior to use without the necessity of any measurement or manipulation thereof by the user. These disposable containers also provide more accurate measurement of mercury and silver alloy than would be possible for the individual user because the large volume of production justifies the use of very precise measuring devices, which devices would be uneconomical for the individual dental surgeon.
These prior art containers generally comprise two chambers and a valve means or constricted opening therebetween closed by a valve closing means or occlusion; each ingredient is isolated in its respective chamber. Mixing is generally effected by movement of the occluding portion along the long axis of the container ("translational") with respect to the opening, thus removing the occlusion and allowing communication between the two chambers. The mercury in the upper chamber is allowed to flow into the lower chamber, the occlusion is replaced, and the ingredients are mixed together by agitating the container in an amalgamator or the like as is well known in the art. Examples of these so-called translational containers are disclosed in Kobernick, U.S. Pat. Nos. 3,139,180; 3,139,181; and 3,357,545.
These translational containers, while providing for the separate storage of accurately premeasured ingredients, are subject to several disadvantages.
First, the translational nature of the removal of the barrier between the two chambers allows droplets of mercury to be retained on the wall of its chamber and thus not be mixed with the silver alloy. This effect is increased because the occluding portion tends to divide the mercury into several discrete portions during storage. Because of the necessity of accurate compounding of the amalgam to effect the desired properties, such incomplete mixing is highly deleterious.
Second, the translational removal is generally effected by either an unscrewing action or a pulling action on a portion of the container. The unscrewing action is both time-consuming and uncertain, in that the user has no physical indication as to the necessary amount of twisting to effect removal of the occlusion. The pulling action is no better, however, both because of the large amount of friction which hinders the pulling and also because of the possibility of completely separating the pulled portion from the rest of the container with concomitant contamination and loss of materials.
Third, the design of these containers creates manufacturing difficulties. Because of the screw mechanism involved in some types, tolerances must be close if effective segregation of the two chambers is to result.
A further disadvantage in prior art capsules concerns the manner in which the lower, silver alloy containing chamber is formed, generally by sliding the open end of a lower cylindrical portion into the open end of the upper, mercury-containing assembly, the two being held together by friction. But when these two are slid together, the air within is strongly compressed by a sort of piston effect. This trapped compressed air may, upon later heating of the capsule during storage, cause the capsule parts to accidentally disassemble, with concomitant loss or mixing of mercury and silver. Such disassembly, in even small quantities of capsules, is highly undesirable.
These difficulties are obviated by the container of the present invention.